Circular Motion

[Cmonkey123]

Circular Motion

I've started playing around with C# again, making simple games and other experiments in the hopes of making more complex interactive programs.

While working on a simple revolving sphere, I realized I can't figure out for the life of me how to make it revolve properly.

Does anyone know what equations or methods or anything I could possibly use to make an object revolve? Any help would be appreciated.

/edit
This is what I have so far (I found this equation for circular motion online, not sure if that's even close to what I want), but it doesn't work:

		public void RotationTimerTick( object sender, System.EventArgs e )
		{
			int x = sphereX;
			int y = sphereY;

			int cos20 = Convert.ToInt32( Math.Cos( 20 ) );

			sphereX = 100 * cos20 + x;
			sphereY = 100 * cos20 + y;

			Invalidate();
		}

Obviously, I then use a draw command to draw the sphere at sphereX, sphereY. This doesn't freeze the program like many of my previous attempts, but the sphere stays at (0,0) and doesn't move anywhere.

 

[TheOutkastDev]

You're casting it to an int. You need to do floats, or doubles because Cos( 20 ) is always less than 1.

 

[Cmonkey123]

Hmm okay, I got the sphere moving.

But now it just moves in a line diagonally to the right...

I wanted the sphere to move on a circle I have drawn in my program with a radius of 100 pixels. Anyone have any ideas?

 

[Serp]

Make Y depend on sin. Oh... and you'll want to cos and sin the same number...

		double number;

		public void RotationTimerTick( object sender, System.EventArgs e )
		{
			number += 0.1;

			sphereX = 100 * Math.Cos(number) + 100;
			sphereY = 100 * Math.Sin(number) + 100;

			Invalidate();
		}

Having basic understanding of trigonometry definately helps, too.

 

[Cmonkey123]

That still makes it go in a diagonal line.

I even tried converting the 20 degrees into radians and it still moves in a line.

Here's what I have so far:

		public void RotationTimerTick( object sender, System.EventArgs e )
		{
			float x = sphereX;
			float y = sphereY;

			sphereX = ( 50 * (float)Math.Cos( 20 ) ) + x;
			sphereY = ( 50 * (float)Math.Sin( 20 ) ) + y;

			Invalidate();
		}

 

[Cmonkey123]

I'm way past trig, but I never learned circular motion... haha.

I think I got it rotating right now, thanks much.

 

[Cmonkey123]

Okay it's rotating, but now I can't get the damn thing to rotate on my circle.

What part of the equation do I have to change to make it start and move on my circle?

Sorry, I probably sound retarded, but this is bugging the crap outta me.

 

[TheOutkastDev]

Multiply the sine and cosine of the angle by the radius of your circle, and add the center point's x and y values to sphereX and sphereY respectively.

 

[Cmonkey123]

Urg!

It's still not working... It keeps rotating off the circle even if I add the center points x and y of the circle to the sin and cos.

Here's the entire script, maybe I'm doing something else wrong:

using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;

namespace rotation_test
{
	public class rotationtest : System.Windows.Forms.Form
	{
		Timer rotationtimer = new Timer();

		Image sphere;
		Bitmap offScreenBuffer;

		float sphereX, sphereY;
		
		double rotationfactor;

		const string sphere_file_name = "..\\..\\sphere.ico";

		private System.ComponentModel.Container components = null;

		public rotationtest()
		{
			sphere = Image.FromFile( sphere_file_name );

			InitializeComponent();
		}

		public void RotationTimerTick( object sender, System.EventArgs e )
		{
			rotationfactor += 0.1;

			sphereX = 100 * (float)Math.Cos( rotationfactor ) + ( ( this.ClientSize.Width / 2 ) - 100 );
			sphereY = 100 * (float)Math.Sin( rotationfactor ) + ( ( this.ClientSize.Height / 2 ) - 100 );

			Invalidate();
		}

		public void DoPaint( Graphics g, PaintEventArgs e )
		{
			System.Drawing.Pen ellipsepen = new Pen( Color.Red, 1 );

			g = e.Graphics;
			base.OnPaint( e );

			g.DrawImage( sphere, sphereX, sphereY );
			g.DrawEllipse( ellipsepen, ( this.ClientSize.Width / 2 ) - 100, ( this.ClientSize.Height / 2 ) - 100, 
				200, 200 ); 
		}

		private void InitializeComponent()
		{
			// 
			// rotationtest
			// 
			this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);
			this.BackColor = System.Drawing.Color.Black;
			this.ClientSize = new System.Drawing.Size(792, 466);
			this.ForeColor = System.Drawing.Color.Black;
			this.MaximumSize = new System.Drawing.Size(800, 500);
			this.MinimumSize = new System.Drawing.Size(800, 500);
			this.Name = "rotationtest";
			this.Text = "rotation test";

			rotationtimer.Enabled = false;
			rotationtimer.Interval = 30;
			rotationtimer.Tick += new System.EventHandler( RotationTimerTick );
		}

		protected override void Dispose( bool disposing )
		{
			if( disposing )
			{
				if (components != null) 
				{
					components.Dispose();
				}
			}
			base.Dispose( disposing );
		}

		protected override void OnKeyDown( KeyEventArgs e )
		{
			string input = e.KeyData.ToString();

			switch( input )
			{
				case "Enter":
					rotationtimer.Enabled = true;
					break;
			}

			Invalidate();
		}

		protected override void OnPaint( PaintEventArgs e )
		{
			Graphics gOffScreen;
			Graphics g = e.Graphics;

			if( offScreenBuffer == null || offScreenBuffer.Width != this.ClientSize.Width || offScreenBuffer.Height != this.ClientSize.Height )
			{
				offScreenBuffer = new Bitmap( this.ClientSize.Width, this.ClientSize.Height );
			}
			
			gOffScreen = Graphics.FromImage( offScreenBuffer );
			DoPaint( gOffScreen, e );
			gOffScreen.Dispose();

			g.DrawImage( offScreenBuffer, 0, 0 );
		}

		[STAThread]
		static void Main() 
		{
			Application.Run( new rotationtest() );
		}
	}
}

 

[David]

lol, sorry man, I tried to get some help for you. My daughter was just exempted from her trig final and I asked her if she could help. All I got was something about living the rest of her life without trig? What's that all about?

 

[Cmonkey123]

Haha, you're telling me

but seriously though, why isn't it working? It should be rotating on the red circle, but it's not; it's about 100 pixels off in the x and y directions... the client size thing/2 -100 should be the right spot, so what's wrong with it?

 

[Kamron]

To get a circle, COS(X) + SIN(Y) = 1 where X and Y are two numbers less than 1.

So COS and SIN of the same number is wrong...

thats my hint to you

If you need more help, please ask.

 

[TheOutkastDev]

To get a circle, COS(X) + SIN(Y) = 1 where X and Y are two numbers less than 1.

So COS and SIN of the same number is wrong...

thats my hint to you

If you need more help, please ask.

its cos(X)^2 + sin(y)^2 = 1

 

[Cmonkey123]

Uh... thanks for the help.

But I made a stupid and simple error, I subtracted 100 from the x and y for the sphere's coordinates and it put it at the wrong spot. Subtracting by 16 instead (the radius of the sphere) put it on the right path.

 

[p4tRi0t3]

from rotation Matrix

Where A is the angle of rotation in degrees and P the coordinate of the sphere
Ra Is the Rotation Matrix
P' is the coordinates of the moved point

      Ra       *  P    =                P'
( CosA -SinA ) * (x)   =   ( (CosA * x) + (-SinA * y ) )
( SinA CosA  ) * (y)   =   ( (SinA * x) + (CosA * y )  )

that's give us :

sphereX = ( (float)Math.Cos( 20 ) * x ) + ( -(float)Math.Sin( 20 ) * y ) + ( ( this.ClientSize.Width / 2 ));
sphereY = ( (float)Math.Sin( 20 ) * x ) + ( (float)Math.Cos( 20 ) * y )+ ( ( this.ClientSize.Height / 2 ));

make your sphere start at

sphereX =this.ClientSize.Width / 2 + 100;
sphereY =this.ClientSize.Height / 2

You should see your sphere in circular motion

 

[Cmonkey123]

I got it figured out a while ago...

Your help is still appreciated though.

 

[Kamron]

its cos(X)^2 + sin(y)^2 = 1

Ya, it was a simple typo... I had the logic correct in my head.

That is the actual formula that you use, correct? Where 1 = the radius, and you change the formula as needed. The formula then turns into X^2 + Y^2 = 2R, blah blah.

I think I provided incorrect information anyways.... Because I realized you wanted it to rotate in a circle. Or did I give correct information?